5150 mk1 issue

[Stormbringer]

Hi, and thanks for letting me be part of your forum. I have a Peavey 5150 Mk1 that I have a bit of a problem with. There is a relatively low frequency hum when the amp is on. It doesn't seem to get any louder as the amp is turned up so its not generic amp hiss and i don't think its an earthing issue either. The performance of the amp doesn't seem to be affected. Anybody have any ideas? I know these amps are world famous for their noise, but it seems worse than just a noisy amp. Any help greatly appreciated.

Dom

 

[Chester Nimitz]

Some ideas could be :

A] filter caps

B] tube issue

C] dirty power IE: line voltage filtering needed.

D] Dirty input/amp jacks

E] Bad ground

 

[SpiderWars]

Always check/suspect tubes first. Start pulling preamp tubes (keeping track of each tube and it's position) and see if the noise goes away.

 

[Stormbringer]

Cheers for for the quick responses I will try those suggestions later.

 

[Racerxrated]

Tubes first, what is your signal route like? Maybe a bad cable somewhere, try straight in with different cables just to eliminate that as a possibility.

 

[CaseyCor]

Does it hum when there's no cable plugged in the front? That would help narrow it down.

 

[misterspockyall]

posting out of interest. My combo does the same. FWIW, I just tested unplugging cable from the input jack, the low freq hum disappeared.